Prevention of dye wandering in



United States Patent PREVENTION OF DYE WANDERING 1N PHOTOGRAPHIC EMULSIONS George D. Hill, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application May 15, 1952, Serial No. 288,031

9 Claims. (Cl. 95--7) This invention relates to photographic silver halide emulsions and more particularly to-photographic silver halide emulsions sensitized with certain optical sensitizing dyes.

It is well known to alter the sensitivity of photographic silver halide emulsions by incorporating therein various.

types of sensitizing dyes, the type depending upon the ultimate purpose of the photographic material. One serious drawback in the use of such optical sensitizing dyes has been their tendency to wander from the emulsion in which they have been incorporated in certain instances. This objection is particularly noticeable in the preparation of mutlilayer photographic materials, or in the preparation of photographic materials giving various degrees of contrast. In these instances, the optical sensitizing dyes have a tendency to migrate from the emulsion in which they have been incorporated into a second emulsion in which their presence is undesirable. For example, when one of the silver halide emulsions in a photographic material giving various degrees of contrast is optically sensitized, while the other emulsion is not, there is a tendency for the optical sensitizing dye to become distributed more or less uniformly throughout both of the photographic emulsions, thus reducing the degree of contrast which can be obtained.

It is, therefore, an object of my invention to provide a method of preventing dye wandering in photographic silver halide emulsions. Another object is to provide a photographic material giving various degrees of contrast, wherein the tendency toward dye wandering is eliminated or materially reduced. Other objects will become apparent from a consideration of the following description and examples.

According to my invention, I realize the above objects by combining the silver nitrate with the water-soluble halide in the presence of an optical sensitizing dye selected from those represented by the following general formula:

R-1 T -L=L .H o =LL 1= 5 c=0 wherein R represents an alkyl group, such as methyl, ethyl,

n-propyl, S-hydroxyethyl, etc., (e. g. an alkyl group of from 1 to 2 carbon atoms), L represents a methine' group, d represents a positive integer of from 1 to 3, n represents a positive integer of from 1 to 2, 2' represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heter0-' "ice droxybenzothiazole, 6-hydroxybenzothiaz0le, etc.), those of the naphthothiazole series (e. g. a-naphthothiazole, finaphthothiazole, 5-methoxy- 3-naphthothiazole, 5-ethoxyfi-naphthothiazole, 7-methoxy-a-naphthothiazole, 8-methoxy-a-naphthothiazole, etc.), those of the thionaphtheno- 7,6,4,5-thiazole series (e. g. 4'-methoxythionaphtheno-7',- 6',4,4-thiazole, etc.), those of the oxazole series (e. g. 4- methyloxazole, 5-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dimethyloxazole, 5- phenyloxazole, etc.), those of the benzoxazole series (e. g. benzoxazole, 5-chlorobenzoxazole, 5-phenylbenzoxazole, S-methylbenzoxazole, 6-methylbenzoxazole, 5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, 5-methoxybenzoxazole, 6-methoxybenzoxazole, S-ethoxybenzoxazole, 6-chlorobenzoxazole, 5-hydr0xybenzoxazole, 6-hydroxybenzoxazole, etc.), those of the naphthoxazole series (e. g. a-naphthoxazole, fi-naphthoxazole, etc.), those of the selenazole series (e. g. 4-methylselenazole, 4-phenylselenazole, etc.), those of the benzoselenazole series (e. g. benzoselenazole, S-chlorobenzoselenazole, S-methoxybenzoselenazole, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, etc.), those of the naphthoselenazole series (e g. a-naphthoselenazole, B-naphthoselenazole, etc.), those of the thiazoline series (e. g. thiazoline, 4-methylthiazoline, etc.), those of the 2-quinoline series (e. g. quinoline, S-methylquinoliue, 7-methylquinoline, 6-chloroquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6- hydroxyqninoline, S-hydroxyquinoline, etc.), those of the 4-quinoline series (e. g. quinoline, 6-methoxyquinoline, 7-methylquinoline, S-methylquinoline, etc.), those of the 3,3 -dialkylindolenine series (e. g. 3,3 -dimethylindolenine, 3,3,5 trimethylindolenine, 3,3,7 trimethylindolenine, etc.), those of the Z-pyridine series (e. g. pyridine, 3-methylpyridine, 4-methylpyridine, S-methylpyridine, 6- methylpyridine, 3,4-dimethylpyridine, 3,5-dirnethylpyridine, 3,6-dimethylpyridine, 4,5-dimethylpyridine, 4,6-dimethylpyridine, 4-chloropyridine, 5-chloropyridine, 6- chloropyridine, 3-hydroxypyridine, 4-hydroxypyridine, 5- hydroxypyridine, 6-hydroxypyridine, 3-phenylpyridine, 4- phenylpyridine, 6-phenylpyridine, etc.), those of the 4- pyridine series (e. g. 2-methylpyridine, 3-methylpyridine, 2-chloropyridine, 3-chloropyridine, 2,3-dimethylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine, Z-hydroxypyridine, 3-hydroxypyridine, etc.), etc., and Q represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, such as a thiazolone nucleus, for example, a 2,4(3,5)-thiazoledione nucleus, such as 2,4(3,5)-thiazoledione, 3-alkyl-2,4(3,5)-thiazolediones (e. g. 3-ethyl-2,4 (3,5) thiazoledione), 3 -phenyl-2,4(3,5)-thiazoledione, 3-a-naphthyl-2,4( 3 ,5) -thiazoledione, a 2-thio-2,4( 3 ,5) thiazoledione (a rhodanine) nucleus, such as a 3-alkyl-2- thio-2,4(3,5)-thiazoledione (3-alkyl-rhodanine) (e. g. 3- ethyl-2-thio-2,4(3,5)-thiazoledione or 3-ethylrhodanine), 3 phenyl 2 thio-2,4(3,5)-thiazoledione (3-phenylrhodanine) or 3-a-naphthyl-2-thio-2,4(3,5)-thiazoledione- (3- a-naphthylrhodanine nuclei or 3-(l-benzothiazyl)-2-thio- 2,4(3,5) thiazoledione (3 (1 benzothiazyl)rhodanine) nuclei, a 2-alkylmercapto-4(5)-thiazolone nucleus, such as 2-ethylmercapto-4(5)thiazolone, a thiazolidone nucleus, such as 4-thiazolidone or its 3-alkyl (e. g. ethyl), 3-phenyl or 3-a-naphthyl derivatives, a 2-alkylphenylamino-4(5)-thiazolone nucleus or a 2-diphenylamino-4(5)- thiazolone nucleus; an oxazolone nucleus, for example, a 2-thio-2,4(3,5)-oxazoledione nucleus, such as a 3-alkyl-2- thio-2,4(3,5)-oxazoledione nucleus (e. g. 3-ethy1-2-thio- 2,4(3,5)-oxazoledione) and a 2-imino-2,4(3,5)-oxazolone (a pseudohydantoin) nucleus; a 2-alkylmercapto-5(4)- imidazolone nucleus, such as 2n-propylmercapto-5-(4)- iinidazolone; a thionaphthenone nucleus, such as 2-(l)- thionaphthenone or 1(2)-thionaphthenone, a pyrazolone nucleus; an oxindole nucleus, such as 2,3-dihydro-3ltetoindole, and like five-rncmbered heterocyclic nuclei; a 2,4,6- triketohexahydropyrirnidine nucleus, for example, barbituric acid or Z-thiobarbituric acid as well as their l-alkyl (e. g. l-ethyl) or l,3-diall yl (e. g. 1,3-diethyl) derivatives; at 3,4-dihydro-2(1)-quinolone nucleus, such as 3,4-dihydro- 2(1)-quinolone (dihydrocarbostyril); a 3,4-dihydro-2(l)- quinoxalone nucleus, such as 3,4-dihydro-2(l)-quinoxalone (oxydihydroquinoxaline); 3-phenomorpholone (1,4,3- benzoxazine-3 (4)-one or benzo-fl-morpholone) nuclei; 1,4,2 benzothiazine-3(4)-one (ketodihydrobenzoparathiazine) nuclei, and the like six-membered heterocyclic nuclei. Thus an optical sensitizing dye is present during the formation of the silver halide and is more strongly adsorbed to the surface of the silver halide range than would be possible through simple mixing after preparation of the washed, finished emulsion. Moreover, I have found that the process of my invention does not extend to the use of other optical sensitizing dyes, such as those of the carbocyanine class. In the preparation of the photographic silver halide emulsions according to my invention, the optical sensitizing dye can be incorporated in either the silver nitrate solution or the solution of watersoluble halide. I have found that it is especially advantageous to incoiporate the optical sensitizing dyes selected from those represented by Formula I above in the aqueous solution of silver nitrate containing a small amount of gelatin, since precipitation of the dye is substantially avoided.

Dyes coming within the scope of Formula 1 above which have been found to be especially useful comprise those represented by the following general formula:

II. Z R2 wherein R, Z and 12 each have the values given above, Q1 has the same values as those assigned above to Q, R1 represents an alkyl group of at least 7 carbon atoms, such as n-heptyl, n-octyl, n-nonyl, n-decyl, n-lauryl, etc., and R2 represents a hydrogen atom, an alkyl group, e. g. methyl, ethyl, etc., or an aryl group, e. g. phenyl, p-tolyl, etc., (e. g. a mononuclear aryl group of the benzene series).

To prepare a photographic silver halide printing material which gives rise to various degrees of contrast under the same conditions of development, it has been proposed to coat in layers, or to mix together, two different silver halide emulsions having different contrasts (gamma). Thus, an emulsion which is capable of giving high contrast and is sensitive to blue (such as a silver chloride emulsion) can be mixed with an emulsion which is capable of giving low contrast and is sensitive to green (such as a spectrally sensitized silver bromide emulsion). If such a composite emulsion is exposed to light passing through a blue-green filter, the emulsion works normally and is suitable for negatives of normal gradation (contrast). If, however, it is desired to print from a negati e with strong contrasts, the light which acts upon the emulsion which is capable of giving high contrast is cut oil by means of a filter permeable only to green, and a normal picture is obtained by means of the emulsion which is capable of giving 10W contrast. If, on the other hand, it is desired to print from a negative with but little contrast, the light which acts upon the emulsion which is capable of giving low contrast is cut off by means of a filter permeable only to blue, and a normal picture is obtained by means of the emulsion which is capable of giving high contrast.

A variation of the above process involves the sensitization of the contrasty chloride emulsion instead of the bromide emulsion of lower contrast, to the green portion of the spectrum.

Advantageously, I incorporate the optical sensitizing dye in the silver halide emulsion of higher contrast, although it is possible to sensitize both emulsions according to my invention.

Typical sensitizing dyes selected from those represented by Formulas I and II above which can advantageously be used in my invention comprise the following, for example:

5-[( 3 ethyl 2(3) benzothiazolylidene)ethylidene] 3 ethylrhodanine.

3 carbethoxymethyl 5 [(3 ethyl 2(3) benzothiazolylidene ethylidene rh odanine.

3 ethyl 5 [(3 ethyl 2(3) bcnzoxazolylidene)- ethylidenehhodanine.

3 ethyl 5 3 ethyl 2(3) benzoxazolylidene)ethylidcne]-lphenyl-2-thiohydantoin.

3 ethyl 5 (1 ethyl 2(1) quinolylidene) 2 thio- 2,4( 3,5)-oxazoledione.

3 ethyl 5 [(3 methyl 2 thiazolinylidene)ethylidene]-2-thio-2,4( 3,5)oxazoledione.

3 ethyl 5 [(3 ethyl 2(3) benzoselenazolylidene)- ethylidene]-2-thio-2,4(3,5 -oxazoledione.

5 (1 ethyl 4(1) quinolylidene) 2- ethylthio-4(5)- thiazolone.

2 diphenylamino 5 [(3 ethyl 2(3) benzothiazolylidene)ethylidcne]-4(5)-thiazolonc.

5 (3 ethyl 2(3) benzothiazolylidene) 1,3 diphenyl- 2-thiohydantoin.

5 [(3 ethyl 2(3) benzoxazolylidene)ethylidene]- l,3-diphenyl-2-thiohydantoin.

3 ethyl 5 [(1 ethyl 2(1) ,8 naphthothiazolylidene) )isopropylidene]rhodanine.

3 ethyl 5 [(3 ethyl 2(3) benzothiazoylidene)isopropylidene] -2-thio-2,4( 3,5) -oxazoledione.

4 3 methyl 2( 3) benzothiazolylidene)ethylidene]- 3-methyl-l-phenyl-S-pyrazolone.

4 [(3 methyl 2(3) benzothiazolylidene) a ethylethylidene]-3-methyl-l-phenyl-S-pyrazolone.

5-(1-ethyl-2( 1 )-pyridylidene)-3-phenylrhodanine.

3 ethyl 5 (3 ethyl 2(3) benzothiazolylidene)rhodanine.

5 [(3 ethyl 2(3) -.benzoxazolylidene)ethylidene] 3- n-heptyl-1-phenyl-2-thiohydantoin.

5 [(1 ethyl 4(1) quinolylidene)ethylidene] 3 nlaurylrhodanine.

5 [(3 methyl 2(3) thiazolinylidene)ethylidene] 3- n-heptylrhodanine.

5 [(3 ethyl 2(3) a naphthoxazolylidene)ethylidene]-3-n-heptyl-1-phenyl-2-thiohydantoin.

5 [(3 ethyl 2(3) benzoxazolylidene)ethylidene] 3- n-heptylrhodanine.

5 [(3 ethyl 2(3) benzoxazolylidcne)ethylidene] 3- n-decyl-1-phenyl-2-thiohydantoin.

5 (3 ethyl 2(3) benzoxazolylidene)isopropylidenel- 3-n-heptylrhodanine.

5 [(3 ethyl 2(3) 0c naphthoxazolylidene)isopropylidene]-3-n-heptyl-1-phenyl-2-thiohydantoin.

5 [(3 methyl 2 thiazolinylidene)ethylidene] 3 nheptyl-1-phenyl-2-thiohydantoin.

5 [4 (3 ethyl 2(3) benzoxazolylidene)butenylidene]-3-n-laurylrhodanine.

5 (3 ethyl 2( 3) benzothiazolylidene) 3 n heptylrhodanine.

The following examples will serve to illustrate the manner whereby I practice my invention.

Example I.The following solutions were prepared: Solution A:

Mixing temperature C Solution B p v Silver nitr g 170 Water cc 340 Mixing temperature; C 60 Solution C:

[(3 ethyl 2(3) benzoxazolylidene)- ethylidene] 3 n heptyl 1 phenyl- 2 thiohydantoin g .025 Acetone cc 25 Mixing temperature C 21 Solution D:

Sodium chloride g 96 Water cc 1440 S-N-hydrochloric acid cc 6 Mixing temperature C 55 Solution E:

Gelatin g 645 Water cc 1470 Potassium iodide g 0.25 Mixing temperature C 75 Solution F:

Potassium iodide g 0.44 Water cc 400 Mixing temperature C 21 Solution B was mixed with Solution A, and Solution C was added. Solution D was dumped into the mixed solutions, and the whole was held for 40 minutes at 60 C. Solution E was then added and the mixture was heated to 70 C. and held at that temperature for minutes. The mixture was then cooled to 60 C. and Solution F was added. The mixture was then cooled, set, shredded, and washed for two hours. The resulting emulsion was of high contrast and it was mixed with an equivalent amount (based on the silver chloride content) of a low contrast, unsensitized silver chloride emulsion. To the mixed emulsions, 100 cc. of per cent formaldehyde were added and the mixture was coated on 2000 square feet of paper. A high contrast print was obtained by exposing through a Wratten No. 12 Filter (i. e. a filter which transmits substantially no light of wavelength shorter than about 495 mu, although there was about 1 per cent transmission of light of wavelength 300 to 340 mu). A low contrast print was obtained by exposing through a Wratten No. 34 Filter (i. e. a filter having its maximum transmission between 315' and 500 mu, with no transmission between 500 mu and 635 mu).

Example 2.-A mixture of silver chloride emulsions was obtained in exactly the same manner as described in 1 above except that 0.025 g. of 5-(3-methyl-2-thiazolinylidene)ethylidene 3 n heptyl 1 phenyl 2 thiohydantoin was used instead of the dye inSolution C of that example. In a similar manner, a high contrast print was obtained by exposing through a Wratten No. 12 Filter and a low contrast print was obtained by exposing through a Wratten No. 34 Filter.

Example 3.--The following solutions were prepared:

Solution A:

Gelatin g 42 Water cc 1700 Mixing temperature C 40 Solution B:

Silver nitrate g 170 Water cc 850 Mixing temperature C 20 Solution C:

5 [(3 ethyl 2(3) benzoxazolylidene)- isopropylidene] 3 n heptylrhodanine g 0.25 Acetone cc Mixing temperature C 20 Solution D:

Solutions C and D were mixed together, and this mix ture along with Solution B was simultaneously added to Solution A over a period of 10 minutes. When the addi tion was complete, Solution E was then added, and the emulsion was finished as described in Example 1 above. The resulting high contrast, optically sensitized emulsion was mixed with an equivalent amount (based on the silver chloride content) of a low contrast unsensitized silver chloride emulsion. To the combined emulsions there were added 100 cc. of 20 per cent formaldehyde, and the mixture was coated on 2000 square feet of paper. A high contrast print was obtained by exposing through a Wratten No. 12 Filter and a low contrast print was obtained through a Wratten No. 34 Filter.

While my invention has been described above in the illustrative examples with particular reference to silver chloride emulsions, it is to be understood that it can be advantageously employed with other photographic silver halide emulsions, e. g. gelatino-silver-chlorobromide, chloriodide, -chlorobromiodide, -bromide, and -bromiodide emulsions, and in particular, developing-out emulsions. Also, mixtures of the various silver halide emulsions can be employed in producing photographic elements of varying contrast. The ratio of the various silver halides in the elements of varying contrasts can also be varied, depending on the degree of contrast desired, speed, etc. For example, one part of a high contrast photographic emulsion of silver chlorobromide (50% silver chloride and 50% silver bromide) sensitized with one of the dyes enumerated above can be mixed with two parts of a low contrast silver chlorobromiodide (6% silver chloride, silver bromide, and 4% silver iodide) emulsion to give a product showing varying degrees of contrast, even after artificial or simulated aging. In like manner, one part of a 50/50 chlorobromide emulsion of high contrast sensitized with one of the optical sensitizing dyes enumerated above can be mixed with two parts of a 20/80 chlorobromide emulsion of lower contrast to give a varying contrast emulsion, showing little or no change on simulated aging.

Various emulsion addenda, such as antifoggants, coating aids, hardeners, and the like, can be incorporated in the silver halide emulsions prepared in accordance with my invention.

In addition to the alkali metal halides used above in preparing silver halides according to my invention, other water-soluble halides, such as the alkaline earth halides, ammonium halides, cadmium halides, etc. can be employed.

My invention is not to be construed as limited to any particular method of emulsion making, except as to the manner of precipitation of the silver halide as described above. For a discussion of the art of emulsion making and an improvement thereof, see British patent 655,082, published July 11, 1951. With the exception of the precipitation step as described above, any of the methods of emulsion making described in the British patent can be used in practicing my invention.

When employing the process of my invention in the preparation of photographic elements showing varying degrees of contrast, the contrast of the emulsion of higher contrast is generally at least 2.5 times that of the emulsion of lower contrast. See, for example, Kridel U. S. Patent 2,358,169, issued September 12, 1944, and Davey and Knott U. S. Patent 2,318,597, issued May 11, 1943.

sensitizing dyes of the type represented by Formulas I and II above have been previously described in one or more of the following U. S. patents: 2,170,804, issued August 29, 1939; 2,l77,4012,177,403, issued October 24, 1939; 2,263,757, issued November 25, 1941; 2,265,908, issued December 9, 1941; and 2,282,116, issued May 5, 1952. See also Carroll U. S. application Serial No. 274,445, filed March 1, 1952 (now U. S. Patent 2,635,961, issued April 21, 1953), copending herewith, for a description of the preparation of such dye types.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. in a process of preparing a mixture of two photographic silver halide emulsions, one of said emulsions being optically sensitized and having a contrast higher than that of the other non-optically sensitized emulsion, the step which comprises combining the silver nitrate with the Water-soluble halide in the presence of an optical sensitizing dye selected from those represented by the following general formula:

//Q\\ n1 f z=L) 1 iJ(=L-L)i i= f :0

wherein R represents an alkyl group, L represents a methine group, d represents a positive integer of from 1 to 3, n represents a positive integer of from 1 to 2, and Z and Q each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from. to 6 atoms in the heterocyclic ring, in the production of the emulsion of higher contrast and thereafter mixing the said emulsion of higher contrast containing the optical sensitizing dye and the said emulsion of lower contrast together.

2. In a process of preparing a mixture of two silver halide emulsions, at least one of the emulsions containing a sensitizing dye so that the emulsions have different spectral sensitivities, one of the emulsions having a contrast at least 2.5 times greater than that of the other emulsion, the steps which comprise admixing an aqueous alkali metal halide solution and an aqueous gelatin solution containing silver nitrate and an optical sensitizing dye selected from those represented by the following general formula:

n-NT-L:L)" f-c (=LL)41=6 wherein R represents an alkyl group, L represents a mcthino group, d represents a positive integer of from 1 to 3, n represents a positive integer of from 1 to 2, and Z and Q each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, in the production of the emulsion of higher contrast, and thereafter mixing together the said optically sensitized emulsion of higher contrast with the said silver halide emulsion of lower contrast.

3. In a process of preparing a mixture of two silver chloride emulsions, at least one of the emulsions containing a sensitizing dye so that the emulsions have different spectral sensitivities, one of the emulsions having a contrast at least 2.5 times greater than that of the other emulsion, the steps which comprise admixing an aqueous alkali metal halide solution and an aqueous gelatin solution containing silver nitrate and an optical sensitizing dye selected from those represented by the following general formula:

ing together the said optically sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

4. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have different spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous alkali metal chloride solution and an aqueous gelatin solution containing silver nitrate and an optical sensitizing dye selected from those represented by the following general formula:

wherein R represents an alkyl group of from 1 to 2 carbon atoms, R1 represents an alkyl group containing at least 7 carbon atoms, R2 represents a member selected from the group consisting of a hydrogen atom, an alkyl group of from 1 to 2 carbon atoms, and a mononuclear aromatic group of the benzene series, n represents a positive integer of from 1 to 2, and Z and Q1 each represents the nonmetallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, in the preparation of the emulsion of higher contrast, and thereafter mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

5. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have different spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous alkali metal chloride solution and an aqueous gelatin solution containing silver nitrate and an optical sensitizing dye selected from those represented by the following general formula:

wherein R represents an alkyl group of from 1 to 2 carbon atoms, R represents a member selected from the group consisting of a hydrogen atom, an alkyl group of from 1 to 2 carbon atoms, and a mononuclear aromatic group of the benzene series, 11 represents a positive integer of from 1 to 2, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the thiazole series, benzothiazole series, a-naphthothiazole series, 3- naphthothiazole series, thiazoline series, oxazole series, benzoxazole series, ot-naphthoxazole series, fl-naphthoxazole series, selenazole series, benzoselenazole series, anaphthoselenazole series, fl-naphthoselenazole series, pyridine series, quinoline series, and 3,3-diall4ylindolenine series, and Q represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the rhodanine series, 2-thiohydantoin series, 2-thio-2,4(3,5)-oxazolcdione series, and 5'pyrazol0ne series, in the preparation of the emulsion of higher contrast, and thereafter mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

6. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have different spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous gelatin solution containing silver nitrate and an aqueous alkali metal chloride solution containing an optical sensitizing dye F I I MW,

9 selected from those represented by the following general formula:

Z R2 n-fi '--oH=cH),.-To=o1rb=6 0:0

wherein R represents an alkyl group of from 1 to 2 car bon atoms, R2 represents a member selected from the group consisting of a hydrogen atom, an alkyl group of from 1 to 2 carbon atoms, and a mononuclear aromatic group of the benzene series, n represents a positive integer of from 1 to 2, Z represents the non-metallic atoms necessary to complete a heterocyclie nucleus selected from the group consisting of those of the thiazole series, benzothiazole series, a-naphthothiazole series, B-naphthm thiazole series, thiazoline series, oxazole series, benzoxazole series, u-naphthoxazole series, fi-naphthoxazole series, selenazole series, benzosclenazole series, a-naphthoselenazole series, fi-naphthoselenazole series, pyridine series, quinoline series, and 3,3-dialkylindolenine series, and Q represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the rhodanine series, Z-thiohydantoin series, 2-thio-2,4(3,5)-oxazoledione series, and S-pyrazolone series, in the preparation of the emulsion of higher contrast, and thereafter mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

7. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have difierent spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous alkali metal chloride solution and an aqueous gelatin solution containing silver nitrate and S-l(3-ethyl-2(3)-benzoxazolylidene)ethylidene]-3-n-heptyl-1-phenyl-2-thiohydantom, in the preparation of the emulsion of higher contrast, and there after mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

8. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have different spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous alkali metal chloride solution and an aqueous gelatin solution containing silver nitrate and 5-[(3-methyl-2-thiazolinylidene)ethylidenel- B-n-heptyl-1-phenyl-2-thiohydantoin, in the preparation of the emulsion of higher contrast, and thereafter mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast. 9. In a process of preparing a mixture of two silver chloride emulsions, one of the emulsions containing a sensitizing dye and the other being unsensitized so that the emulsions have different spectral sensitivities, the sensitized emulsion having a contrast at least 2.5 times greater than that of the unsensitized emulsion, the steps which comprise admixing an aqueous gelatin solution containing silver nitrate and an aqueous alkali metal chloride solution containing 5 (3-ethyl-2 3 -benzoxazolylidene) isopropylidene]-3-n-heptylrhodanine in the preparation of the emulsion of higher contrast, and thereafter mixing together the said sensitized emulsion of higher contrast with the said silver chloride emulsion of lower contrast.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,928 Mannes et a1. Apr. 9, 1935 2,202,026 Renwick May 28, 1940 2,235,426 Goodman Mar. 18, 1941 2,284,877 Martinez June 2, 1942 2,464,780 Anish Mar. 22, 1949 FOREIGN PATENTS 326,287 Great Britain Mar. 13, 1930 503,845 Great Britain Apr. 14, 1939 OTHER REFERENCES Eder: Ausfiihrliches Handbuch der Photographie,

Band II, 1. Teil (1927), entitled Die Grundlagen der photographischen Negativverfahren, by Luppo-Cramer, pages 24-28. 

1. IN A PROCESS OF PREPARING A MIXTURE OF TWO PHOTOGRAPHIC SILVER HALIDE EMULSIONS, ONE OF SAID EMULSIONS BEING OPTICALLY SENSITIZED AND HAVING A CONTRAST HIGHER THAN THAT OF THE OTHER NON-OPTICALLY SENSITIZED EMULSION, THE STEP WHICH COMPRISES COMBINING THE SILVER NITRATE WITH THE WATER-SOLUBLE HALIDE IN THE PRESENCE OF AN OPTICAL SENSITIZING DYE SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 